This project continues to investigate the role played by the compliant properties of the neuromuscular system in the control of voluntary movement as well as in the response of the system to applied perturbations. We suggest that these are not separable properties because many if not most "perturbations" are actually generated by the interaction forces between different body segments during the performance of voluntary motor tasks. This is true, even when in terms of "intention", a movement involves only one of a few segments. The limb is viewed as a visco-elastic-inertial system, moving under the influence of forces originating from neurally controlled muscle activation, gravity and external perturbation, Neural activation of the muscles not only generates accelerating forces but also directly alters the visco-elastic properties of the peripheral neuromuscular apparatus. This affect on neuromuscular visco-elasticity is caused both by direct changes to muscle mechanical properties and by complex changes to reflex excitability. Our studies over the last nine years and more, have focused on action about a single joint (the elbow and the ankle). We propose here to continue these single-joint studies but to start to broaden the investigation to multi-joint, planar movements. Experiments using a diverse set of perturbations of the limb will be performed. We will use our knowledge of single-joint behavior, both as an initial model for multi-joint behavior, and as a behavioral template, deviations from which can be better discerned. However, multi-joint movement is inherently more complex than single-joint movement in its physical description. We can expect that the neurological mechanisms that control it will also be more complex and as a result, we do not expect that the mechanisms described for single-joint control will be sufficient for multi-joint control. However, we do assume that they provide a useful point of departure for further exploration.